Relationship design patterns in GraphQL - Practice Problems & Coding Challenges

Challenge - 5 Problems

❓ query_result

intermediate

Output of a One-to-Many Relationship Query

Given a GraphQL schema where Author has many Books, what is the output of this query?

query {
  authors {
    name
    books {
      title
    }
  }
}

Assume the data has one author named "Alice" with two books titled "GraphQL Basics" and "Advanced GraphQL".

GraphQL

query {
  authors {
    name
    books {
      title
    }
  }
}

A {"data":{"authors":[{"name":"Alice","books":[]}]} }

B {"data":{"authors":[{"name":"Alice"}]}}

C {"data":{"authors":[{"name":"Alice","books":[{"title":"GraphQL Basics"},{"title":"Advanced GraphQL"}]}]}}

D {"errors":[{"message":"Field 'books' not found on type 'Author'"}]}

💡 Hint

Think about how one-to-many relationships return nested lists in GraphQL.

The query requests each author's name and their list of books with titles. Since Alice has two books, both appear nested under her.

🧠 Conceptual

intermediate

Identifying Relationship Types in GraphQL Schema

Which of the following GraphQL field definitions best represents a many-to-many relationship between Student and Course?

A type Student { courses: [Course!]! } and type Course { students: [Student!]! }

B type Student { course: Course } and type Course { student: Student }

C type Student { courses: Course } and type Course { students: Student }

D type Student { courses: Course! } and type Course { students: Student! }

💡 Hint

Many-to-many means each side can have multiple related items.

Option A uses lists on both sides, indicating multiple courses per student and multiple students per course, which is many-to-many.

📝 Syntax

advanced

Correct Syntax for One-to-One Relationship Field

Which option shows the correct GraphQL syntax for a one-to-one relationship where a User has one Profile?

A type User { profile: Profile! }

B type User { profiles: [Profile] }

C type User { profile: [Profile!]! }

D type User { profile: Profile }

💡 Hint

One-to-one means exactly one related item, not a list.

Option A declares the profile field as non-nullable single Profile, matching one-to-one.

❓ optimization

advanced

Optimizing Nested Relationship Queries

You have a GraphQL query fetching Posts with their Comments and each comment's Author. Which approach reduces over-fetching and improves performance?

A Fetch all fields of Posts, Comments, and Authors without selection sets.

B Use fragments to select only needed fields for Comments and Authors.

C Fetch Posts only and query Comments and Authors in separate queries.

D Fetch Posts with Comments but omit Authors to reduce data.

💡 Hint

Fragments help reuse and limit fields fetched.

Using fragments to select only necessary fields avoids fetching unnecessary data and improves query efficiency.

🔧 Debug

expert

Debugging Circular Relationship Query Error

Given a GraphQL schema where Employee has a manager who is also an Employee, this query causes an error:

query {
  employees {
    name
    manager {
      name
      manager {
        name
      }
    }
  }
}

What is the most likely cause of the error?

A The query syntax is invalid because nested fields are not allowed.

B The 'manager' field is not defined on Employee type.

C The 'name' field is missing from the Employee type.

D The query causes infinite recursion due to circular references without depth limit.

💡 Hint

Think about how recursive relationships can cause problems in queries.

Querying nested managers repeatedly without limiting depth can cause infinite recursion or stack overflow errors.